Use of catheter balloons is widespread in medical dilation procedures. Coronary angioplasty is a typical dilation procedure whereby a catheter having a balloon at its distal end is inserted into a coronary artery exhibiting occlusion. The catheter is positioned such that the balloon is adjacent the occluding stenosis. The balloon is then inflated by injecting a fluid into the balloon via the catheter. The inflated balloon exerts an outward pressure against the stenosis, thereby dilating the artery and alleviating the occlusion.
A critical performance requirement for the balloon is that it have sufficient structural integrity to inflate against the force of the stenosis without rupturing. In many cases the resistive force of the stenosis is substantial and the balloon requires a substantial inflation pressure to overcome this force. It is, thus, apparent that the balloon must be fabricated from a high-integrity material to avoid rupturing while dilating the artery. Consequently, the choice of material from which to fabricate the balloon is critical to the success of the dilation procedure.
Certain high molecular weight polymeric materials have been found to possess the properties necessary to perform as catheter balloons for coronary angioplasty. These properties include thinness, flexibility, and strength. Polymeric materials having a biaxial orientation have been found to be particularly effective because of their high integrity, i.e., high tensile strength and uniformity. Thus, certain biaxially oriented polymers are the material of choice for fabrication of catheter balloons. Manufacture of polymeric materials having a biaxial orientation requires a specific, but well known, molding and stretching process.
Catheter balloons are generally formed in a configuration which fits over a catheter with the catheter passing axially through the balloon. The balloon is tapered at the ends where its walls join the catheter and is wide in the body where its walls radially diverge from the catheter. Unfortunately, it has been found that when polymeric balloons are formed in this configuration, it is virtually impossible to achieve uniform biaxial orientation of the polymer throughout the entire balloon. In particular, it has been found that biaxial orientation of the polymer can be achieved substantially throughout the body of the balloon, but that the tapered ends terminating at the catheter lack biaxial orientation, adopting either a unilateral or random orientation. As a result, the tapered ends of balloons lack the structural integrity of the balloon body and are prone to failure during operation even though the balloons themselves are conventionally termed "biaxially oriented balloons."
In recognition of this problem, a biaxially oriented polymeric balloon is needed having high structural integrity uniformly across the balloon walls including the tapered ends of the balloon. Further, a method is needed whereby the structural integrity of a biaxially oriented polymeric balloon can be enhanced, particularly at the tapered ends of the balloon.